The present invention generally pertains to frequency synthesis and is particularly directed to an improved frequency synthesizer for use in a broadcast telephone system in which information signals are communicated over an assigned frequency channel.
Frequency synthesizers typically include one or more phase-locked loops for generating a signal having a given frequency. Multiple interdependent phase-locked loops are used to improve frequency resolution.
In a broadcast telephone system it is desirable to have the capability of being able to assign any given broadcast to one of a plurality of different frequency channels.
In typical off-the-shelf commercially available frequency synthesizers the frequency is assigned by manual adjustment of controls, such as push buttons or the like. However, a broadcast telephone system typically includes far more subscribers than available frequency channels, and it is preferred that the frequency for any given broadcast be assigned automatically in accordance with availability.
Also, when a typical off-the-shelf commercially available frequency synthesizer is used in a broadcast telephone system, phase noise and electronic noise due to microphonics are introduced into the frequency synthesizer. The term "microphonics" refers to the induction of electrical signals as a result of sound waves such as are introduced by mechanical vibrations, such as those caused by cooling fans.